On Saturday, anti-vivisectionists targeted David Jentsch, a neuroscientist at the University of California in Los Angeles, by setting fire to his car outside his house. It's the latest in a wave of attacks against California researchers and despite the FBI investigating, no-one has been arrested.

To give you a flavour of the kind of intimidation these scientists are facing in their daily lives, here's a quote from their statement:

We will come for you when you least expect it and do a lot more damanage (sic) than to your property. Where ever you go and what ever you do we'll be watching you as long as you continue to do your disgusting experiments.

It's repulsive stuff, and I don't just mean the spelling. That the FBI are not able to track these people down swiftly is staggering. We are not talking about criminal masterminds here.

The text above did remind me of a former journalism lecturer who taught my class the first law of thuggery. No one who's really going to attack you warns you they're going to do it first, he assured us. And he should know.

The spate of attacks against UCLA researchers began in 2006, when the ALF tried to leave a Molotov cocktail on the doorstep of a university psychiatrist, but got the wrong house. Since then, other attacks have included more fire bombs and sticking a hose through a broken window and flooding a house.

Britain brought in new laws to clamp down on animal rights extremists in 2005, but in spite of them, threats and intimidation continue against staff at companies linked to Huntingdon Life Sciences. A year later, in 2006, US Congress passed the Animal Enterprise Terrorism Act, which in California at least, seems to be similarly inadequate.

Is it the detail of law that is lacking here, or are police forces understaffed, undermotivated or insufficiently funded to arrest these people?